<html>
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>dlgamma</title>
  </head>
  <body bgcolor="#FFFFFF">
    <center>Scilab Function</center>
    <div align="right">Last update : September 1997</div>
    <p>
      <b>dlgamma</b> -   derivative  of gammaln function, psi function</p>
    <h3>
      <font color="blue">Calling Sequence</font>
    </h3>
    <dl>
      <dd>
        <tt> y = dlgamma(x)  </tt>
      </dd>
    </dl>
    <h3>
      <font color="blue">Parameters</font>
    </h3>
    <ul>
      <li>
        <tt>
          <b>x</b>
        </tt>: real vector</li>
      <li>
        <tt>
          <b>y</b>
        </tt>: real vector with same size.</li>
    </ul>
    <h3>
      <font color="blue">Description</font>
    </h3>
    <p>
      <tt>
        <b>dlgamma(x)</b>
      </tt> evaluates, at all the elements of <tt>
        <b>x</b>
      </tt> the logarithmic 
    derivative of the gamma function which corresponds also to the derivative of the
    gammaln function :</p>
    <pre>

         d/dx (gamma(x)) / gamma(x) = d/dx (ln gamma(x))
     
    </pre>
    <p>
      <tt>
        <b>x</b>
      </tt> must be real. Also known as the psi function.</p>
    <h3>
      <font color="blue">Examples</font>
    </h3>
    <pre>

dlgamma(0.5)

 
  </pre>
    <h3>
      <font color="blue">See Also</font>
    </h3>
    <p>
      <a href="gamma.htm">
        <tt>
          <b>gamma</b>
        </tt>
      </a>,&nbsp;&nbsp;<a href="gammaln.htm">
        <tt>
          <b>gammaln</b>
        </tt>
      </a>,&nbsp;&nbsp;</p>
    <h3>
      <font color="blue">Author</font>
    </h3>
    <p>W. J. Cody (code from Netlib (specfun))</p>
  </body>
</html>
